As a folder, all my systems (a sr-2/l5639 rig, a celeron/mini-itx combo running two gtx 460 2win and my main i7 970@4,2 ghz/gtx 295 rig) are running 24/7!
Noise, well, speak louder, i can't hear you!
Heat: with an open window and 0c outside temp, it's 27c inside my living room...
Power: at 7...